Compression/expansion process that allows temperature to vary independent of pressure

ABSTRACT

Systems and methods are described herein to operate an air compression and/or expansion system in its most efficient regime, at a desired efficiency, and/or achieve a desired pressure ratio independent of discharge temperature, with little to no impact on thermal efficiency. For example, systems and methods are provided for controlling and operating hydraulic pumps/motors used within a hydraulically actuated device/system, such as, for example, a gas compression and/or expansion energy system, in its most efficient regime, continuously, substantially continuously, intermittently, or varied throughout an operating cycle or stroke of the system to achieve any desired pressure and temperature profile. Such systems and methods can achieve any desired pressure ratio independent of input or discharge temperature, and can also achieve any desired discharge temperature independent of pressure ratio, without altering any of the structural components of the device or system.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of U.S. ProvisionalPatent Application Ser. No. 61/432,945, entitled “Compression/ExpansionProcess That Allows Temperature to Vary Independent of Pressure,” filedJan. 14, 2011, the disclosure of which is hereby incorporated byreference herein in its entirety.

BACKGROUND

The invention relates generally to devices, systems and methods for thecompression and/or expansion of a gas, such as air, and particularly tosuch a device that allows the temperature of the gas to be variedindependently of its pressure during compression and/or expansion.

Devices and systems used to compress and/or expand a gas, such as air,and/or to pressurize and/or pump a liquid, such as water, can generateheat during, for example, a compression process. Adiabatic compressionassumes that no energy (heat) is transferred to or from the gas duringthe compression, and all supplied work is added to the internal energyof the gas, resulting in increases of temperature and pressure. Theincrease in temperature means compression does not follow a simplepressure to volume ratio. Although adiabatic compression is lessefficient, it is a very fast process for compressing a gas. An aircompressor can achieve near adiabatic compression and expansion when thecompressor has good insulation, a large gas volume, and/or a relativelyfast compression stroke. In practice, there will always be a certainamount of heat flow out of the compressed gas to the compressor itselfThus, making a perfect adiabatic compressor would require perfect heatinsulation of all parts of the machine.

In contrast to adiabatic compression, isothermal compression assumesthat the compressed gas remains at a constant temperature throughout thecompression or expansion process. During the compression cycle, energyis removed from the system at the same rate as heat is added by themechanical work of compression. An air compressor can achieve nearisothermal compression when the compressor has a large heat exchangingsurface, a small gas volume, and/or a relatively slow compressionstroke. In practice, there will always be a certain amount of heat flowinto the compressed gas, resulting in an increased temperature of thegas.

Since perfect isothermal compression is generally not attainable withconventional compression technologies, known compressor systems have amulti-stage compressor that may include intercoolers that cool airbetween stages of compression and/or after-coolers that cool air aftercompression. In such a system, however, the air may still achievesubstantial temperatures during each stage of compression, prior tobeing cooled, which will introduce inefficiencies in the system. Forexample, unless an infinite number of compression stages withcorresponding intercoolers are used, perfect isothermal compressioncannot be achieved.

Since perfect adiabatic and isothermal compression are not practical, apolytropic model is used to measure real-world results. This model takesinto account both a rise in temperature in the gas as well as some lossof energy (heat) to the compressor's components. This assumes that heatmay enter or leave the system, and that input shaft work can appear asboth increased pressure (usually useful work) and increased temperatureabove adiabatic (usually losses due to cycle efficiency). Compressionefficiency is then the ratio of the actual temperature rise (polytropic)vs. theoretical 100 percent (adiabatic).

For a given gas volume reduction (i.e., ratio of final volume to initialvolume), an adiabatic compression process results in the highest finalgas pressure, the highest final gas temperature, and the highest workconsumption. In contrast, for the same volume reduction, an isothermalcompression process results in the lowest final pressure, lowest finalgas temperature (i.e. the same as the starting temperature), and lowestwork consumption. Processes that involve levels of heat flowintermediate to those in adiabatic (zero heat flow) and isothermal(maximum heat flow), result in intermediate values of gas pressure, gastemperature, and work consumption. Those skilled in the art willrecognize that a perfectly isothermal air compression process is atheoretical extreme that can only be achieved in reality by involving arelatively cold heat sink; regardless it is a useful metric for aircompression/expansion discussion and analysis. While it is possible toprovide cooling or heating to have a discharge temperature lower thanthe inlet during a compression process (or vice versa for an expansionprocess), the theoretical extremes discussed here assume no heat removalor addition using a separate cycle (such as a Rankine or heat enginecycle) is employed to increase heat transfer to or from the process.

Compression and/or expansion systems and related thermodynamic processesare usually designed to have a target temperature and pressure at theinput or output of the system, whether that process involves expansionor compression. Generally, a design output pressure is achieved using acompressor/expander device and the desired temperature is adjusted withan after treatment such as, for example, a cooler or a heater. Processesthat use a series of compressor/expander devices (stages) withintercoolers between each stage that cool the gas between stages ofcompression and/or after coolers that cool the gas after the finalcompression stage come closest to achieving isothermal compression.These multi-stage systems are really no different than a singlecompression/expansion device except that several are placed in series toachieve a higher output pressure or accept a higher input pressure(depending on the desired function of the system) at a differentdischarge temperature than would have been achieved with a single stage.The temperature achieved after the compression or expansion process is afunction solely of the pressure ratio and isentropic/polytropicefficiency for adiabatic compression, and cannot be optimizedindependently from the pressure ratio.

Other processes, such as oil flooded screw compressors, can achieve alower discharge temperature by cooling during the compression process,however this result is secondary to the primary function of the oil as alubricant for the rotors. Such devices cannot independently tailor thedischarge temperature and pressure, and are specified primarily basedupon delivery pressure. After treatments such as, for example, a cooleror a heater, are still required to deliver the process fluid at therequired temperature.

Having to deal separately with temperature and pressure requirements ofa process fluid is a product of the fact that, for a given pressureratio, temperature is a function purely of the isentropic efficiency ofthe device. No heat transfer is built into the process as a specificfunction of the device (in contrast to devices such as screw compressorsdescribed above, where the reduced discharge temperature is a byproductof the sealing the oil provides). Popular design methodology suggestsreducing the discharge temperature (for compression or expansion) is adesired goal insofar as it indicates an increase in isentropicefficiency. The reason for this design methodology is that conventionalcompression systems and processes are not capable of decouplingtemperature from pressure.

A compression/expansion process that can achieve a desired pressureratio independent of discharge temperature, with little to no impact onthermal efficiency would be very valuable to modern industry andrepresents a novel and unparalleled approach to compression andexpansion.

SUMMARY OF THE INVENTION

Systems and methods are described herein to operate an air compressionand/or expansion system in its most efficient regime, at a desiredefficiency, and/or achieve a desired pressure ratio independent ofdischarge temperature, with little to no impact on thermal efficiency.For example, systems and methods are provided for controlling andoperating hydraulic pumps/motors used within a hydraulically actuateddevice/system, such as, for example, a gas compression and/or expansionenergy system, in its most efficient regime, continuously, substantiallycontinuously, intermittently, or varied throughout an operating cycle orstroke of the system to achieve any desired pressure and temperatureprofile. In such a system, a variety of different operating regimes canbe used depending on the desired output gas pressure and the desiredstored pressure of the compressed gas. Hydraulic cylinders used to driveworking pistons within the system can be selectively actuated and/or canbe actuated to achieve varying force outputs to incrementally increasethe gas pressure, within the system for a given cycle. Such systems andmethods can achieve any desired pressure ratio independent of input ordischarge temperature, and can also achieve any desired dischargetemperature independent of pressure ratio, without altering any of thestructural components of the device or system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a compression and/or expansiondevice according to an embodiment.

FIG. 2 shows a single stage of one embodiment of an air compression andexpansion system.

FIG. 3A is a schematic illustration of a portion of another embodimentof an air compression and expansion system.

FIG. 3B is a schematic illustration of a portion of the air compressionand expansion system of FIG. 3A illustrating a system controller andhydraulic pump.

FIGS. 4A and 4B are each a schematic illustration of a portion of anactuator of the air compression and expansion system of FIG. 3.

FIG. 4C is a side view of a portion of an actuator of the system of FIG.3.

FIG. 4D is a cross sectional view taken along line 4D-4D in FIG. 4C.

FIG. 4E is an end view taken along line 4E-4E in FIG. 4C.

FIG. 4F is a cross sectional view taken along line 4F-4F in FIG. 4C.

FIGS. 5-11 are each an example graph illustrating the operation of acompression and/or expansion device according to an embodiment.

FIG. 12 is a schematic illustration of a compression and/or expansiondevice, according to another embodiment.

DETAILED DESCRIPTION

Systems, methods and devices used to compress and/or expand a gas, suchas air, and/or to pressurize and/or pump a liquid, such as water, aredescribed herein. Such devices and systems can be used, for example,within a compressed air energy storage (CAES) system. In somecompression and/or expansion devices and systems, a hydraulic actuatorcan be used to move or compress a gas within a pressure vessel. Forexample, an actuator can move a liquid within a pressure vessel suchthat the liquid compresses the gas in the pressure vessel. Suchcompression devices and systems are described in U.S. patent applicationSer. No. 12/785,086; U.S. patent application Ser. No. 12/785,093; andU.S. patent application Ser. No. 12/785,100, each titled “Compressorand/or Expander Device” (collectively referred to as “the Compressorand/or Expander Device applications”), incorporated herein by referencein their entirety. The Compressor and/or Expander Device applicationsdescribe a CAES system that can include multiple stages of compressionand/or expansion. Other examples of devices and systems for expandingand/or compressing as gas are described in U.S. Provisional patentapplication Ser. No. 12/977,724, to Ingersoll et. al. (“the Ingersoll Iapplication”), entitled “System and Methods for Optimizing efficiency ofa Hydraulically Actuated System,” the disclosure of which isincorporated herein by reference in its entirety.

In some compression and/or expansion devices and systems, one or morehydraulic pumps/motors can be used to move (or be moved by) gas andliquid within the system, and systems and methods are described hereinto operate the hydraulic pump/motor in its most efficient regime,continuously, substantially continuously, intermittently, or variedthroughout an operating cycle or stroke of the system to achieve anydesired pressure and temperature profile. Compression and/or expansiondevices and systems can have efficient or optimal operating ranges thatcan vary as a function of, for example, mass flow rate, pressure,temperature, overall system efficiency, among other parameters. Systemsand methods are provided that allow the hydraulic pumps/motors to beoperated as a function of any given parameter (e.g. gas inlettemperature, gas outlet temperature, inlet pressure, outlet pressure,pressure ratio, system efficiency, etc.) throughout the stroke or cycleof the gas compression and/or expansion system to achieve any desiredpressure and temperature profile.

As described herein, devices and systems used to compress and/or expanda gas, such as air, and/or to pressurize and/or pump a liquid, such aswater, can release and/or absorb heat during, for example, a compressionor expansion process, using one or more heat transfer mechanisms. Suchsystems and methods as described herein, can be used to operate a gascompression and/or expansion system in its most efficient regime, at adesired efficiency, and/or to achieve a desired pressure ratioindependent of discharge temperature, with little to no impact onthermal efficiency.

In some embodiments, the devices and systems described herein can beconfigured for use only as a compressor. For example, in someembodiments, a compressor device described herein can be used as acompressor in a natural gas pipeline, a natural gas storage compressor,or any other industrial application that requires compression of a gas.In another example, a compressor device described herein can be used forcompressing carbon dioxide. For example, carbon dioxide can becompressed in a process for use in enhanced oil recovery or for use incarbon sequestration.

In some embodiments, the devices and systems described herein can beconfigured for use only as an expansion device. For example, anexpansion device as described herein can be used to generateelectricity. In some embodiments, an expansion device as describedherein can be used in a natural gas transmission and distributionsystem. For example, at the intersection of a high pressure (e.g., 500psi) transmission system and a low pressure (e.g., 50 psi) distributionsystem, energy can be released where the pressure is stepped down fromthe high pressure to a low pressure. An expansion device as describedherein can use the pressure drop to generate electricity. In otherembodiments, an expansion device as described herein can be used inother gas systems to harness the energy from high to low pressureregulation.

In some embodiments, a compression and/or expansion device as describedherein can be used in an air separation unit. In one exampleapplication, in an air separator, a compression and/or expansion devicecan be used in a process to liquefy a gas. For example, air can becompressed until it liquefies and the various constituents of the aircan be separated based on their differing boiling points. In anotherexample application, a compression and/or expansion device can be usedin an air separator co-located with in a steel mill where oxygenseparated from the other components of air is added to a blast furnaceto increase the burn temperature.

In some embodiments, a compression and/or expansion device as describedherein can be used in a chemical reaction process. In one exampleapplication, the compressor and/or expansion device can be the reactionvessel in a chemical reaction process. Some chemical reactions only takeplace at a certain temperature, pressure, range of temperatures, orrange of temperatures. For example, gas and/or liquid reactants in thecompression and/or expansion device can be maintained at a certaintemperature or with in a certain temperature range by changing thepressure in the compression and/or expansion device. The temperature ofthe gas and/or liquid reactants can be changed over time by changing thepressure in the compression and/or expansion device as the reactionproceeds. In another example application, the rate of a reaction canalso be a function of temperature and/or pressure. Thus, the reactionrate can be maximized, minimized, or optimized for other factors (e.g.,selectivity or efficiency) by changing the temperature and/or pressurein the compression and/or expansion device.

A compression and/or expansion system as described herein can includeone or multiple stages of compression and/or expansion. For example, asystem can include a single stage compression/expansion device, twostages, three stages, etc. Each stage of compression/expansion can havea variety of different configurations and can include one or moreactuators that are used to compress/expand a gas (e.g. air) within acompression/expansion device. In some embodiments, an actuator caninclude one or more pump/motor systems, such as for example, one or morehydraulic pumps/motors and/or one or more pneumatic pumps/motors thatcan be use to move, or be moved by, one or more fluids within the systembetween various water pumps/motors and pressure vessels. As used herein,“fluid” can mean a liquid, gas, vapor, suspension, aerosol, or anycombination thereof. The Compressor and/or Expander Device applicationsincorporated by reference above describe various compression andexpansion systems in which the systems and methods described herein canbe employed.

As described herein, in some embodiments of a gas compression and/orexpansion system, hydraulic pumps/motors can be used to drive (or bedriven by) one or more hydraulic actuators, which in turn can drive (orbe driven by) a working piston. The working piston can act on (or beacted on by) a gas contained in a working chamber to compress or expandthe gas, directly, or indirectly through a liquid disposed between theworking piston and the gas in the working chamber. As used herein theterm “piston” is not limited to pistons of circular cross-section, butcan include pistons with a cross-section of a triangular, rectangular,or other multi-sided shape.

In some embodiments, a hydraulic actuator as described herein can beused to drive, or be driven by, a working piston within, for example, awater pump/motor, to move water (or other liquid) in and out of theworking chamber of a pressure vessel used to compress and/or expand agas, such as air, contained in the working chamber. Although particularembodiments of an actuator are described herein to drive, or be drivenby, a water pump/motor and/or a compression and/or expansion device, itshould be understood that the various embodiments and configurations ofan actuator can be used to drive, or be driven by, a working pistonwithin a water pump, a compression and expansion device, a compressiondevice, an expansion device, any other device in which a working pistonis used to move a fluid, and/or any device to which motive force can beapplied or from which motive force can be received.

The loads applied to the working piston(s) can be varied during a givencycle of the system. For example, selectively establishing fluidcommunication between the hydraulic pump/motor(s) and differenthydraulic pistons, and/or different surfaces of the hydraulic piston(s),in the hydraulic actuator(s), the ratio of the net working surface areaof the hydraulic actuator(s) to the working surface area of the workingpiston acting on the gas in the working chamber can be varied. Thus, theratio of the pressure of the hydraulic fluid provided by (or receivedby) the hydraulic pump/motor to the pressure of the gas in the workingchamber can be varied during a given cycle or stroke of the system. Astate in which a hydraulic actuator has a particular piston area ratio(e.g., the ratio of the net working surface area of the hydraulicactuator to the working surface area of the working piston acting on, orbeing acted on by, the gas in a working chamber) at a given time periodcan be referred to herein as a “gear,” and a change in from one state toanother state can be referred to herein as a “gear change.” In addition,the number of working pistons/working chambers and hydraulic actuatorscan be varied as well as the number of piston area ratio changes withina given cycle.

As described herein, heat energy can be removed from a gas during acompression process (or can be added to a gas during an expansionprocess) via a liquid that is present in one or more pressure vessels ofa compressor/expander device to control the gas temperature throughoutthe process. The heat energy can be transferred between the gas and theliquid, the compressor/expander device, and/or a heat transfer elementdisposed within the working chamber. This allows an operator to modifythe amount of energy that is added or removed throughout the process(depending on whether the process is compressing or expanding), therebyachieving a desired pressure ratio independent of temperature. This canbe done in a manner that has very little impact on thermal efficiency,in order to make the temperature control capability of the processtransparent to the performance and cost of the device.

In some embodiments, a heat transfer element can be positioned withinthe interior of a working chamber of a compressor/expander device thatcan provide sufficient gas/liquid interface and/or sufficient thermalcapacity to efficiently intermediate in, and enhance, the transfer ofheat between the gas and the liquid. The heat transfer element canprovide for an increased heat transfer area both with gas that is beingcompressed and with gas that is being expanded (either through angas/liquid interface area or gas/heat transfer element interface), whileallowing the exterior structure and overall shape and size of a workingchamber/pressure vessel to be optimized for other considerations, suchas pressure limits and/or shipping size limitations. The heat transferelement can be a variety of different configurations, shapes, sizes,structures, etc. to provide a relatively high surface area per unitvolume or mass with the gas as it is being compressed/expanded and/or atan end of the stroke of a compression/expansion cycle. The heat transferelement can be formed from one or more of a variety of differentmaterials that provide a relatively high volumetric specific heat ascompared to the gas. The combined effects of density, volume andspecific heat, and how these parameters behave per unit volume, cancontribute to the absorption performance of a particular heat transferelement. For example, both water and various metals provide a relativelyhigh volumetric specific heat as compared to air, particularly atatmospheric air density. Thus, when the metal or water absorbs the heatfrom the air as it is begin compressed, the air and/or water temperatureincreases only moderately. Such heat transfer elements are described inU.S. patent application Ser. No. 12/977,679; titled “Methods and Devicesfor Optimizing Heat Transfer within a Compression and/or ExpansionDevice,” (“the Ingersoll II application”), the disclosure of which isincorporated herein by reference in its entirety.

The use of a liquid (such as water) as a medium through which heatpasses during compression and/or expansion may allow for a continuouscooling process during compression and may provide a mechanism by whichheat may be moved in and/or out of the compression vessel. It canprovide the reverse during expansion. A liquid can have a relativelyhigh thermal capacity as compared to a gas (such as air) such that atransfer of an amount of heat energy from the gas to the liquid producesa significant decrease in the temperature of the gas but only a modestincrease in the temperature of the liquid. This allows buffering of thesystem from substantial temperature changes.

Heat that is transferred between the gas and liquid or components of thecompressor/expander device itself may be moved from or to the workingchamber through one or more heat exchangers that are in contact with theliquid or components of the compressor/expander device. That is, duringcompression the liquid may receive heat from gas that is beingcompressed, and pass this heat to the external environment continuously,both while gas is being compressed and while gas is being received bythe working chamber for later compression. Similarly, heat addition mayoccur when a compressor/expander device is operating in an expansionmode both during expansion and as expanded gas is passed from a pressurevessel. Thus, the liquid within a working chamber can be used totransfer heat from gas that is compressed (or to gas that is expanded)and can also act in combination with a heat exchanger to transfer heatto an external environment (or from an external environment).

As described herein, a gas compression and/or expansion system can havea heat removal process that can be varied independent of processconditions. For example, different pressure ratios (i.e., ratio ofinitial pressure to final pressure in a compression cycle) will resultin different heat energy fluxes within the device. Therefore, the devicecan include a heat transfer system or methods that allow heat to betransferred out of the process fluid regardless of the heat energy fluxand fluid pressure. One type of heat exchanger that can be used toaccomplish this is a heat pipe as described in the Compressor and/orExpander Device applications and the Ingersoll I applicationincorporated by reference above.

In some embodiments, as a liquid (such as water) is moved into a workingchamber to compress a gas (such as air), if there is relatively littlevertical mixing of the liquid, a temperature gradient can be establishedin the liquid, with the highest (during compression, or lowest, duringexpansion, of the gas) temperature at the gas/liquid interface. Thus,the layer of liquid at the top of the liquid column (closest to thegas/liquid interface) will contain a higher proportion of the heatenergy received from the gas during compression (or has given up ahigher proportion of the heat energy to the gas during expansion) thanthe remainder of the liquid. A portion of this top layer of liquid canbe removed from the working chamber after the compression or expansioncycle has been completed, and transferred to another stage of the systemand/or out of the system entirely.

In some embodiments, a gas compression/expansion system can havevariable displacement capability. As a liquid (such as water) is movedinto a pressure vessel, a gas (such as air) is compressed at a rateproportional to the displacement of the liquid. The flow of liquid intothe pressure vessel can be stopped at any time during the compressionstroke once a predetermined pressure is achieved. In this manner, thepressure ratio can be modified quickly and easily, while the dischargetemperature can be maintained at a desired value by changing the heattransfer characteristics within the system. During subsequentcompression cycles, the flow of liquid into the pressure vessel can bestopped at the same time to achieve the same displacement or can bechanged to increase or decrease the displacement depending on any of anumber of variables such as, for example, pressure vessel parametersincluding pressure, temperature and thermal efficiency, systemparameters including pressures upstream or downstream of the pressurevessel (i.e., earlier or later compression stages of the system),overall system efficiency and electricity generation, and power gridparameters including electricity price, electricity supply/demand andgrid stability. Thus, in addition to the compression and expansionsystem being capably of varying temperature independent of pressure, thereverse is also true and the system is capable of varying pressureindependent of temperature. When such systems are paired in series toachieve higher pressures (called a staged process), the pressure ratiowithin each system can be changed by varying the stroke and amount ofwater displaced to not only change the discharge pressure, but alsochange the distribution of work and heat transfer in each. In thismanner, not only is the pressure and temperature of the whole processindependently variable, but the pressure and temperature within eachstage can be varied as well.

FIG. 1 schematically illustrates a portion of a compression and/orexpansion device (also referred to herein as “compression/expansiondevice”) according to an embodiment. A compression/expansion device 100can include one or more pressure vessels 120 (also referred to herein as“cylinder”) having a working chamber 140, an actuator 122 by which thevolume of working chamber 140, and/or the portion of the volume of theworking chamber 140 that can be occupied by gas, can be changed(decreased to compress the gas, increased to expand the gas), and one ormore heat transfer elements 124 disposed within the working chamber 140.The compression/expansion device 100 can be used, for example, tocompress or expand a gas, such as air, within the working chamber 140.The device provides the flexibility of being able to vary temperatureindependent of pressure and pressure independent of temperature withoutintroducing significant penalties to efficiency and performance. Thedevice 100 integrates thermal management with pressure ratio managementsuch that separate devices are not required to vary either parameter.

The pressure vessel 120 can include one or more gas inlet/outletconduits 130 in fluid communication with the working chamber 140.Optionally, the pressure vessel 120 can include one or more liquidinlet/outlet conduits 128 in fluid communication with the workingchamber 140. The working chamber 140 can contain at various time periodsduring a compression and/or expansion cycle, a quantity of gas (e.g.,air) that can be communicated to and from working chamber 140 via theinlet/outlet conduits 130, and optionally can also contain a quantity ofliquid (e.g., water) that can be communicated to and from workingchamber 140 via the inlet/outlet conduits 128. The compression/expansiondevice 100 can also include multiple valves (not shown in FIG. 1)coupled to the inlet/outlet conduits 128, 130 and/or to the pressurevessel 120. The valves can be configured to operatively open and closethe fluid communication to and from the working chamber 140. Examples ofuse of such valves are described in more detail in the Compressor and/orExpander Device applications incorporated by reference above.

The actuator 122 can be any suitable mechanism for selectively changingthe volume of the working chamber 140 and/or the portion of the volumeof the working chamber that can be occupied by gas. For example, theworking chamber 140 can be defined by a cylinder and the face of apiston (not shown in FIG. 1) disposed for reciprocal movement within thecylinder. Movement of the piston in one direction would reduce thevolume of the working chamber 140, thus compressing gas contained in theworking chamber 140, while movement of the piston in the other directionwould increase the volume of the working chamber 140, thus expanding gascontained in the working chamber 140. The actuator can thus be thepiston and a suitable device for moving the piston within the cylinder,such as a pneumatic or hydraulic actuator such as, for example, thehydraulic actuators described in the Ingersoll I applicationincorporated by reference above.

In some embodiments, the working chamber can have a fixed volume, i.e. avolume defined by a chamber with fixed boundaries, and the portion ofthe volume of the working chamber 140 that can be occupied by gas can bechanged by introducing a liquid into, or removing a liquid from, theworking chamber 140. Thus, the working chamber 140 has a volume with afirst portion containing a volume of liquid, and a second portion thatcan contain gas, which volume is the total volume of the working chamber140 less the volume of the first portion (the volume of the liquid). Insuch embodiments, the actuator 122 can be any suitable device forintroducing liquid into, or removing liquid from, the working chamber,such as a hydraulic actuator that can move a liquid in and out of theworking chamber 140 via liquid inlet/outlet conduit 128. In such anembodiment, the actuator 122 can include a water pump (not shown) thatdrives a hydraulically driven piston (not shown) disposed within ahousing (not shown) and can be driven with one or more hydraulic pumps(not shown) to move a volume of liquid in and out of the working chamber140. An example of such a hydraulic actuator is described in theCompressor and/or Expander Device applications incorporated by referenceabove.

In some embodiments, the working chamber can be configured to combinethe techniques described above, i.e. the working chamber can have avariable volume, e.g. using a cylinder and piston as described above,and the portion of the variable volume that can be occupied by gas canbe changed by introducing liquid into, or removing a liquid from, theworking chamber. In another embodiment, a constant volume of liquid canbe maintained in the variable volume working chamber throughout all, ora portion, of the compression cycle. As described above, in someembodiments, the working chamber 140 can contain a liquid, and/or theactuator 122 can be used to change the portion of the working chamber140 that is available to contain gas, by moving a liquid (such as water)into and out of the working chamber, such that gas (such as air) withinthe working chamber 140 is compressed by the liquid. In suchembodiments, depending on the rate at which the working chamber 140 isfilled with liquid, and the heat transfer properties of the heattransfer element 124, the gas and the heat transfer element 124 will berelatively closer or farther from thermal equilibrium, and thus, duringsome or all of the compression cycle, the liquid in the working chamber140 can be caused to contact the heat transfer element 124 to receivefrom the heat transfer element 124 heat energy it received from thecompressed gas. Optionally, the volume may be decreased by a mechanicalpiston directly such as in a reciprocating compressor with a reducedvolume of water disposed within the chamber for the purpose of effectingheat transfer. Optionally, at the end of the compression cycle, anypressurized gas remaining in the working chamber 140 can be releasedfrom the working chamber 140, and transferred to the next step or stagein the compression process or to a storage facility. Liquid can then bemoved into the working chamber 140, to substantially fill the volumeoccupied by gas that was released from the working chamber 140 aftercompression (which volume is now filled with gas at a lower pressure) byintroducing more liquid and/or by reducing the volume of the workingchamber (e.g. by moving a piston). The heat energy stored in the heattransfer element 124 can then be transferred (again, by conductiveand/or convective transfer) to the water in the working chamber 140.

In some embodiments, the working chamber 140 can be partially filledwith a liquid (e.g. water) that can be communicated to and from theworking chamber 140 via the inlet conduit 128 and the outlet conduit130, respectively, or via other conduits (not shown). During thecompression cycle, heat energy generated during the compression processcan be transferred from the gas, to the heat transfer element 124, andthen to the liquid. A volume of the heated liquid can then be dischargedfrom the pressure vessel 120 via the outlet conduit 130 or via aseparate liquid discharge conduit (not shown). As described above withrespect to the heat transfer element 124, the volume of liquid thatoccupies a portion of working chamber 140 reduces the remaining volumeof the working chamber 140 available for a mass of gas to be compressed.In other words, although the liquid in the working chamber 140 providesa mechanism by which the heat energy generated by the compression of thegas can be removed from the pressure vessel 120 (i.e. by first quenchingthe heat transfer element 124 to transfer the heat energy to the liquid,and then discharging the heated liquid out of the pressure vessel 120),both the liquid and the heat transfer element occupy a portion of theworking chamber 140, thereby reducing the mass of gas that can becompressed. In some embodiments, the heat transfer element and thevolume of liquid in the working chamber 140 can be designed to remove asufficient amount of heat energy generated during the compressionprocess, while maximizing the amount of gas in the working chamber 140to be compressed. For example, having multiple heat transfer elements124 that are movable with respect to each other such that the density ofthe heat transfer element 124 disposed in the portion of the workingchamber containing gas can be varied throughout a compression cycle canreduce the volume of liquid for quenching the heat transfer element 124.

Heat energy transferred from the gas to the heat transfer element 124can in turn be transferred out of the pressure vessel 120 by anysuitable means, include a heat pipe, circulating fluid, etc., to alocation where it can be dissipated, used in other processes, and/orstored for future use in the compression/expansion device (e.g. in anexpansion cycle). In addition, or alternatively, heat energy transferredfrom the gas to the heat transfer element 124 can be transferred fromthe heat transfer element 124 to fluid contained in the working chamber140. The heat energy can then be transferred from the fluid out of thepressure vessel. Similar techniques can be used to transfer heat energyfrom outside the pressure vessel to the heat transfer element 124 andthence to the gas in the working chamber, e.g. during an expansioncycle.

The heat transfer element 124 can be a variety of differentconfigurations, shapes, sizes, structures, etc. to provide a relativelyhigh surface area per unit volume or mass that can be in contact withthe gas (e.g., air) as it is being compressed or expanded within theworking chamber 140. In some embodiments, it may be desirable to includea heat transfer element 124 that can be formed with a material that canprovide high thermal conductivity in a transverse and a longitudinaldirection within the working chamber 140. The heat transfer element 124can be formed from one or more of a variety of different materials. Forexample, the heat transfer element 124 can be formed with metals (e.g.stainless steel), metal wires, hybrid wires, carbon fiber,nano-materials, and composite materials (e.g. carbon polymer compounds)which have anti-corrosion properties, are lighter weight, and are lessexpensive than some metallic materials.

The heat transfer element 124 can be disposed at various locationswithin the working chamber 140 so as to optimize the heat transferwithin the pressure vessel 120. For example, in some embodiments, theheat transfer element 124 can be disposed within the working chamber 140near an end portion of the working chamber 140 in a portion occupied bythe gas (e.g., air) near the end of a compression cycle. As the gas iscompressed during the compression cycle, the work done on the gas addsheat energy to the gas. The heat energy is continuously transferred(primarily by conductive and/or convective, rather than radiant, heattransfer) to the heat transfer element 124. This transfer maintains thegas temperature at a lower value than would be the case without the heattransfer element 124, and moderately increases the temperature of theheat transfer element 124. Other examples of heat transfer elements andsystems that can be used to optimize heat transfer are described in theIngersoll II application incorporated by reference above.

FIG. 2 illustrates a portion of a compressed gas storage system 200 thatincludes a compressor/expander device 220 and an actuator 212. Thecompressor/expander device 220 illustrates a single stage of acompressed gas storage system. The compressor/expander device 220includes a first pressure vessel 224 and a second pressure vessel 226.The first and second pressure vessels 224, 226 are each coupled fluidlyto the actuator 212 by a conduit or housing 228 and 230, respectively.The actuator 212 can include a water pump that includes a hydraulicallydriven piston 232. The piston 232 is disposed within a housing orreservoir 240 and can be driven with one or more hydraulic pumps (notshown in FIG. 2) to move toward and away from the conduit 228 of firstpressure vessel 224 to alternately reduce and then increase the portionof the internal volume of the first pressure vessel 224 available tocontain gas (with an equivalent, but opposite increase and reduction ofthe portion of the volume of the second pressure vessel 226 available tocontain gas). Each of the first and second pressure vessels 224, 226 areat least partially filled with a liquid, such as water, that is moved bythe actuator 212 to alternately compress and drive gas from the volumeof each of the first and second pressure vessels 224, 226, when operatedin a compression mode, or to be moved by compressed gas received ineither of the first and second pressure vessels 224, 226 when operatedin an expansion mode.

Each pressure vessel 224, 226 can be considered to define a workingchamber for compressing and/or expanding a gas. The working chamber hasa volume that is defined by the volume of the pressure vessel. Theworking chamber has a portion of this volume that can contain gas and aportion that contains liquid—the portion of the volume that contains gasis equal to the total volume of the working chamber less the volume ofthe portion containing liquid. Operation of the water pump to urgeliquid from the pump cylinder into the pressure vessel reduces thevolume of the portion of the working chamber that can contain gas, thuscompressing the gas contained in that portion (e.g. during a compressioncycle). Similarly, operation of the water pump to allow liquid to betransferred from the pressure vessel to the water pump increases thevolume of the portion of the working chamber that can contain gas,allowing the gas to expand. Alternatively, a working chamber can beconsidered to be defined by the pressure vessel and the portion of thewater pump in fluidic communication with the pressure vessel (i.e. onone side of the working piston), and any conduit or other volumeconnecting the pressure vessel and the water pump. So defined, theworking chamber has a variable volume, which volume can be changed bymovement of the working piston. A portion of the variable volume can beoccupied by liquid (e.g. water), while the remaining portion can beoccupied by gas (e.g. air). The pressure of the gas contained in theworking chamber is essentially equal to the pressure of any liquidcontained in the working chamber, and to the pressure acting on thecorresponding side or face of the working piston.

The compressor/expander device 220 may also include fins, dividersand/or trays 234 that can be positioned within the interior of the firstand second pressure vessels 224, 226. The dividers 234 can increase theoverall area within a pressure vessel that is in direct or indirectcontact with gas, which can improve heat transfer. The dividers 234 canprovide for an increased heat transfer area with both gas that is beingcompressed and gas that is being expanded (either through an gas/liquidinterface area or gas/divider interface), while allowing the exteriorstructure and overall shape and size of a pressure vessel to beoptimized for other considerations, such as pressure limits and/orshipping size limitations.

In this embodiment, the dividers 234 are arranged in a stackconfiguration within the first and second pressure vessels 224 and 226.Each divider 234 can be configured to retain a pocket of gas. In oneillustrative embodiment, each of the dividers 234 can include an upperwall, a downwardly extending side wall that may conform in shape andsubstantially in size to the inner wall of the pressure vessel, and anopen bottom. The open bottom of each of the dividers 234 face in acommon, substantially downward direction when the pressure vessel isoriented for operation. It is to be appreciated that although thefigures show dividers that conform in size and shape to the interior ofthe pressure vessels 224, 226, and are generally shaped similarly to oneanother, other configurations are also possible and contemplated,including embodiments that include dividers that are substantiallysmaller in width than the interior of a pressure vessel and/or that areshaped and sized differently than one another, among otherconfigurations. Various other shapes and configurations of dividers canbe used, such as, for example, the dividers that are shown and describedin U.S. Provisional App. No. 61/216,942 and the Compressor and/orExpander Device applications incorporated by reference above.

As shown in FIG. 2, a manifold 236 can extend centrally through thestack of dividers 234 and fluidly couple each of the dividers 234 to aninlet/outlet port 238 of the pressure vessels 224, 226. In otherembodiments, the manifold may include multiple tubes and/or may belocated peripherally about the stack of dividers or in other positions.Gas may enter and/or exit the pressure vessels 224, 226 through theports 238, and can provide a conduit for fluid communication betweenpockets of gas associated with each divider 234. In other embodiments,such as those in which dividers do not retain a pocket of gas, themanifold may not be included.

As discussed above, heat can be transferred from and/or to gas that iscompressed and/or expanded by liquid (e.g., water) within a pressurevessel. A gas/liquid or gas/divider interface (e.g., provided in part bydividers discussed above) may move and/or change shape during acompression and/or expansion process in a pressure vessel. This movementand/or shape change may provide a compressor/expander device with a heattransfer surface that can accommodate the changing shape of the internalareas of a pressure vessel through which heat is transferred duringcompression and/or expansion. In some embodiments, the liquid may allowthe volume of gas remaining in a pressure vessel after compression to benearly eliminated or completely eliminated (i.e., zero clearancevolume).

A liquid (such as water) can have a relatively high thermal capacity ascompared to a gas (such as air) such that a transfer of heat energy fromthe gas to the liquid significantly decreases the temperature rise ofthe gas but incurs only a modest increase in the temperature of theliquid. This allows buffering of the system from substantial temperaturechanges. Heat that is transferred between the gas and liquid orcomponents of the vessel itself may be moved from or to the pressurevessel through one or more heat exchangers that are in contact with theliquid or components of the vessel. One type of heat exchanger that canbe used to accomplish this is a heat pipe, as discussed in greaterdetail below.

Thus, the liquid within a pressure vessel can be used to transfer heatfrom air that is compressed (or to air that is expanded) and can alsoact in combination with a heat exchanger to transfer heat to an externalenvironment (or from an external environment). By way of example, asshown in FIG. 2, a heat exchanger that includes a circular array of heatpipes 242 that extend through a wall of the pressure vessels 224 and 226and can contact both the liquid within the vessels and the externalenvironment. The heat pipes 242 are just one example embodiment of atype of heat exchanger that can be used to transfer heat to or fromliquid of a pressure vessel. It should be understood that other types ofheat exchangers and other heat pipe configurations can alternatively beused. For example, other heat management devices can be used(alternatively or in addition to) such as, for example, fins, pins,convection-inducing shapes, and/or swirl-inducing shapes, etc.

The embodiment of FIG. 2 is one example of an arrangement of pressurevessels and an actuator that can be used within a gas compression andstorage system. It should be understood, that other arrangements arealso possible and contemplated. By way of example, although the actuatoris shown as including a single, double acting piston that is orientedvertically, other embodiments may include housings with actuators thatinclude horizontally oriented pistons and/or multiple hydraulic pistonsthat operate in parallel to move fluid within working chambers.According to some embodiments, actuators may lack pistons altogether andinstead comprise pumps that move fluid into and out of the pressurevessels. Multiple pumps and/or pistons can additionally, oralternatively, be used in parallel to move fluid into and out of thepressure vessels, according to some embodiments. Still, according toother embodiments, an actuator, such as a hydraulic piston, may have adirect mechanical connection to the motor/generator of the system, asembodiments of the system are not limited to that shown in the figures.Another embodiment can combine the water pump 212 with the pressurevessel 220 such that the mechanical piston moves within the pressurevessel.

FIGS. 3A-3B illustrate schematically an example of a two-stage gasenergy compression and expansion system 300. FIG. 3A is a schematicillustration of a portion of the system 300. Stage one includes a pairof pressure vessels 324, 326 connected in fluid communication to anactuator 312. For example, various types of conduit or housing (as shownin FIG. 3A) can be used to fluidically couple various components of theactuator 312 to the pressure vessels. The pressure vessels 324, 326 caneach include dividers or tray (not shown in FIG. 3A) as described abovefor previous embodiments. The actuator 312 includes liquid pumps drivenby hydraulic actuators or cylinders as described below. As shown in FIG.3A, the actuator 312 includes liquid pumps 344A, 344B and 346. In thisembodiment, liquid pumps 344A and 344B are constructed in two portionsto reduce the height of the pumping equipment, and in this embodimentliquid pumps 344A and 344B act in concert as a single pump. Each of theliquid pumps 344A, 344B and 346 include a liquid piston, or workingpiston, that is hydraulically driven with a pair of hydraulic cylinders.Liquid pump 344A is coupled to and driven by hydraulic cylinders 352 and354; liquid pump 344B is coupled to and driven by hydraulic cylinders356 and 358; and liquid pump 346 is coupled to and driven by hydrauliccylinders 348 and 350. A common drive rod couples the liquid pistons totheir respective hydraulic cylinders. The hydraulic cylinders for stageone can all be controlled by a first high efficiency hydraulic pump 314as shown in FIG. 3B. A hydraulic pump/motor, such as, for example, anArtemis Digital Displacement hydraulic pump manufactured by ArtemisIntelligent Power Ltd. can be used. Other examples of hydraulic pumpsthat can be used are described in U.S. Pat. No. 7,001,158, entitled“Digital Fluid Pump,” and in U.S. Pat. No. 5,259,738, entitled“Fluid-Working Machine,” the entire disclosures of which are herebyincorporated by reference.

As shown in FIG. 3B, a system controller or hydraulic controller 316 canbe used to operate and control the hydraulic pump/motor 314. Thehydraulic pump/motor 314 can be connected to each end of the hydrauliccylinders associated with the various liquid pumps (or workingactuators) of the system. A valve is coupled between each end (i.e. eachhydraulic chamber) of the hydraulic cylinders and the hydraulic pump,which can be selectively opened and closed, e.g. under control of thehydraulic controller 316, to fluidically couple or fluidically isolate,respectively, the output of the hydraulic pump 314 and each hydraulicchamber of each hydraulic cylinder to selectively actuate a specifichydraulic cylinder and, more particularly, a particular side (e.g.,blind side and/or rod side, as described in more detail below) of thehydraulic piston in the specific hydraulic cylinder. Each valve isdesignated by 318 in FIG. 3B.

As shown in FIG. 3A, stage two of the system 300 includes a pair ofpressure vessels 362 and 364 connected in fluid communication to anactuator 313 that includes liquid pumps 366 and 368. As with the stageone configuration, each of the pressure vessels 362 and 364 can includedividers and each of the liquid pumps 366 and 368 include a liquidpiston that is hydraulically driven by (or, in expansion mode, drives) apair of hydraulic cylinders, also shown in FIG. 3A. Liquid pump 366 iscoupled to and driven by hydraulic cylinders 370 and 372 and liquid pump368 is coupled to and driven by hydraulic cylinders 374 and 376. Thehydraulic cylinders for stage two can all be driven by, or drive asecond high efficiency hydraulic pump/motor (not shown) in a similarfashion as stage one, using the same hydraulic controller 316, or asecond hydraulic controller (not shown). It is to be appreciated thatthe stage two hydraulic cylinders can be driven by, or drive variousconfigurations of hydraulic pump/motor, and that the system 300 canhave, for example, one, two, three, four, or more hydraulic pump/motors.

Each of the first and second pressure vessels 324 and 326 of the firststage are fluidly coupled to the pressure vessels 362 and 364 of thesecond stage by a conduit that may include one or more valves (not shownin FIG. 3A) to selectively open and close fluid communication betweenthe volumes of the corresponding pressure vessels. The first and secondpressure vessels 324 and 326 of stage one can also each include a valve(not shown) that opens to allow the receipt of air from the environment(e.g., at atmospheric pressure) or air that has been optionallypre-compressed from atmospheric pressure to a desired pressure, forexample, 1-3 bar. Additional valves can be used between the pressurevessels of stage two and a storage structure or cavern (not shown) inwhich the compressed air from the system may be stored. Valves can becoupled to and disposed at locations along the conduit connecting thevarious components or directly to the components.

FIGS. 4A-4F illustrate an example of a portion of an actuator of a gascompression and expansion system 300. FIG. 4A schematically illustratesthe various components of a portion of actuator 312 including the liquidpump 346, and its corresponding hydraulic cylinders 348 and 350; andFIG. 4B schematically illustrates the various components of thehydraulic cylinder 348. It should be understood, however, that each ofthe liquid pumps and hydraulic cylinders in both the first stage and thesecond stage of the system 300 can be similarly constructed and functionin the same manner as liquid pump 346 and hydraulic cylinder 348. Asshown in FIG. 4A, the liquid pump 346 includes a cylindrical liquidreservoir or housing 382 that can contain liquid, such as, for example,water W (though other working liquids could be used), a liquid piston,or working piston, 374 and a drive rod 376 coupled to the piston 374.The drive rod 376 is also coupled to hydraulic drive pistons 378 and 380of the hydraulic cylinders 348 and 350, respectively. Thus, thehydraulic cylinders 348 and 350 can be used to operate or drive thepiston 374 back and forth within the housing 382, pressurizing andmoving the liquid W contained therein. The liquid housing 382 is dividedinto two portions, one on each side of piston 374. Each portion is influid communication with a pressure vessel, such as the pressure vesselsdescribed above (not shown in FIG. 4A). As described above, each side ofworking piston 374 bears the same pressure as that of the gas containedin the pressure vessel with which that side of working piston 374 boundsa working chamber containing the air.

FIG. 4B schematically illustrates the hydraulic cylinder 348. As shownin FIG. 4B, the hydraulic cylinder 348 includes a cylindrical housing384 in which a hydraulic drive piston 378 is movably disposed. As statedabove, the drive piston 378 is coupled to the drive rod 376. Within thehousing 384 of the hydraulic cylinder 348, hydraulic fluid Hf can bepumped in and out, as will be described in more detail below.

The housing 384 of the hydraulic cylinder 348 defines an interior volumethat is divided into two portions at any given time during a stroke ofthe hydraulic cylinder by the drive piston or hydraulic piston 378. Asshown in FIG. 4B, the portion of the interior volume within the housing384 above the drive piston 378 (or on the opposite side of the piston378 from the rod 376) is referred to herein as the “blind side” or “boreside” Bs, and the portion of the interior volume within the housing 384shown below the drive piston 378 (or on the same side as the rod 376) isreferred to herein as the rod side Rs. To drive the hydraulic cylinders,hydraulic fluid Hf can be pumped into each hydraulic cylinder on either(or both) sides of the drive piston to achieve varying pressures andflow rates within the system. For example, at various steps in theprocess of compressing air for energy storage, the pressurized hydraulicfluid Hf can be pumped into the housing 384 only on the blind side Bs,only on the rod side Rs, or on both sides, depending on the desiredoutput pressure, flow rate and/or direction of force desired at thevarious steps of a compression or expansion cycle.

For example, referring to the liquid pump 346 and its associatedhydraulic cylinders 348 and 350, to move the working piston 374 withinthe housing 382 to change the volume of the working chamber bounded inpart by the working piston, one or both of the hydraulic cylinders 348and 350 can be actuated at a given time period to provide the desiredforce to move the piston. For example, to move the piston 374 upward,hydraulic fluid can be pumped into the blind side, or both the blindside and the rod side of the hydraulic cylinder 350, or hydraulic fluidcan be pumped into the rod side of the hydraulic cylinder 348, or acombination thereof To move the piston 374 downward, hydraulic fluid canbe pumped into the blind side of hydraulic cylinder 348, both the blindside and the rod side of the hydraulic cylinder 348, or the rod side ofthe hydraulic cylinder 350, or a combination thereof Each of these modeshas a different total area of hydraulic piston bearing the pressure ofthe hydraulic fluid, and thus will exert a different force on theworking piston 374. It is to be appreciated that varying the pressure ofthe hydraulic fluid can act in concert with the varying combinations ofreservoir pressurization to provide a wide range of force to move thepiston.

The system 300 can be configured to operate within a desired energyefficiency range of the hydraulic pump(s). The operating pressure rangeof the hydraulic pump(s) and the ratio of surface areas of the liquidpistons to the hydraulic drive pistons (also referred to herein as“piston ratio”) can be used to determine an optimal operating sequencefor the compression process. In addition, by varying which hydraulicpump(s) is actuated to move a liquid piston at a particular point in thecycle, the pressure in the system can be further varied. The pump has apreferred range of pressure and flow, within which it can becontinuously operated as the air piston strokes.

As shown, for example, in FIGS. 4C-4F, the liquid piston 374 has anoperating surface 390 that has a surface area SA_(w) that is the same onboth sides of the liquid piston (i.e. the annular area bounded by theouter perimeter of the liquid piston 374 and the outer perimeter of therod 376), and the hydraulic drive piston 378 has an operating surface392 on the blind side with surface area SA_(b) (i.e. the circularsurface area bounded only by the outer perimeter of the hydraulic drivepiston) and an operating surface 394 on the rod side with a surface areaSA_(r) (i.e. the annular area bounded by the outer perimeter of thehydraulic drive piston and the outer perimeter of the rod). Theoperating surface area of a piston is the surface area of the piston onwhich force is exerted by hydraulic fluid pressure. Thus, when ahydraulic cylinder is actuated by communicating pressurized hydraulicfluid to the blind side, the effective surface area of the hydraulicpiston is greater than when the same pressure is communicated to the rodside (i.e., SA_(b)>SA_(r)). Thus, for a given hydraulic fluid pressure,more force is applied to the rod 376 (albeit in different directions)when the hydraulic fluid pressure is applied to the blind side than whenit is applied to the rod side. It is also possible to generate yet adifferent amount of force for a given hydraulic pressure by applying thehydraulic fluid pressure to both sides of a piston. In this mode ofoperation, referred to as a regenerative mode, the net piston area isequal to the difference between the blind side area SA_(b) and the rodside area SA_(r). This net area corresponds to the cross-sectional areaof the rod, and is referred to as SA_((b-r)).

In some embodiments, a combination of surface areas associated withhydraulic drive piston 378 and hydraulic drive piston 380 arepressurized to achieve a desired output force on rod 376, which maycorrespond to a second pressure of liquid W. The effective or netoperating surface area A_(net) being pressurized for a given gear isthen equal to the sum of the surface areas associated with the variousportions of the hydraulic cylinders 348 and 350 being pressurized withhydraulic fluid. The sum of the surface areas can also be referred to asthe surface area of the hydraulic piston(s) SA_(h). It is to beappreciated that other embodiments include those in which the hydraulicfluid pressure communicated to the various surface areas in actuator 312may be different from each other.

The ratio of the surface area of the working piston or liquid pistonSA_(w) to the surface area of the hydraulic piston(s) SA_(h) dictatesthe hydraulic pressure needed to achieve a desired liquid pressure, andthus gas pressure, at a given point in the cycle. By varying the surfacearea ratio for a given liquid pump/hydraulic cylinder set, varyinglevels of liquid pressure can be achieved at different points within thecompression cycle for the same levels of hydraulic pressure. Thepressure of the hydraulic fluid needed to achieve a particular liquidpressure (and/or gas pressure) can be calculated as follows.

F _(h) (force of hydraulic fluid)=P _(h) (hydraulic pressure)×SA _(h)(SA _(r) or SA _(b) or SA _((b-r))

F _(w) (force applied to liquid)=P _(w) (liquid pressure)×SA _(w)

F_(h)=F_(w)

P _(w) ×SA _(w) =P _(h) ×SA _(h)

P _(w) =P _(h)×(SA _(h) /SA _(w)) and P _(h) =P _(w)×(SA _(w) /SA _(h))

A maximum and minimum operating pressure for each hydraulic pump can beestablished, e.g. as the limits of a range of operating pressure withinwhich the hydraulic pump operates at or above a desired energyefficiency. This pressure range can be used to determine the pistonratio (e.g., (SA_(h)/SA_(w))) needed at various points during acompression cycle to operate the system so as to approach or achieveoperation within the maximum efficiency range of the hydraulic pump. Forexample, for a hydraulic pump having a maximum efficient operatingpressure of 300 bar and a desired maximum output pressure of the air(and therefore the liquid) is 30 bar, the piston ratio (i.e.,(SA_(w)/SA_(h))) required at the end of the pressurization cycle, whenthe liquid and gas pressure reaches 30 bar, is 10:1. Correspondingly, ifthe hydraulic pump has a minimum efficient operating pressure of 120bar, and the air enters the system at 3 bar, then the piston ratio(i.e., (SA_(w)/SA_(h))) required at the start of the pressurizationcycle, when the liquid and gas pressure is 3 bar, is 40:1. The number ofliquid pumps and hydraulic pumps needed, and the piston ratios (andcorresponding size of the hydraulic cylinders and liquid pumps) for thevarious liquid pump/hydraulic sets can then be determined such that thesystem can operate within the desired efficiency range for the entirecompression cycle (i.e., compressing the gas from 3 bar to 30 bar).There are a variety of different operating sequences that can be used toincrementally increase the pressure in the system and to achieve thisoutput. It is understood that the approach can be applied usinghydraulic pumps with maximum operating pressures higher or lower than300 bar, and minimum operating pressures higher or lower than 120 bar.

At a given time during a compression or expansion cycle, the actuator312 can be referred to as being in a particular “state” or gear that isassociated with the piston area ratios being pressurized within theactuator at that time. As described above, when the system makes achange in the ratio of the pressure of the hydraulic fluid in thehydraulic actuator to the pressure of the liquid in the liquid pump(s)actuated by the hydraulic actuator (i.e., the ratio of the pressurizedsurface area of the liquid piston to the net operating pressurizedsurface area(s) of the hydraulic piston(s) actuating the liquid piston)this is referred to as a “gear shift” or “gear change.” There is avariety of different combinations or sequences of gear changes (changesin piston area ratios) that can be incorporated into a particularoperating sequence of the system.

In the example of system 300, where each liquid pump has two identicalassociated hydraulic cylinders to actuate the liquid pump, there aresixteen possible states for the two actuators, i.e. every combination ofeach chamber being pressurized or not pressurized (two states for fourchambers gives 2⁴ combinations). For identical hydraulic cylinders (i.e.in which the blind side area of each cylinder is the same and the rodside area of each cylinder is the same), there are four differentpossible gears (with associated piston area ratios) that can be used toactuate each working or liquid piston in each direction. For example, tomove a liquid piston upward in one liquid pump, hydraulic fluid can bepumped into (1) the rod side of the upper hydraulic cylinder (or the rodside of the upper hydraulic cylinder and the blind side of bothcylinders, which cancel each other out), (2) the blind side of the lowerhydraulic cylinder (or the blind side of the lower cylinder and the rodside of both cylinders, which cancel each other out), (3) both the blindside and the rod side of the lower hydraulic cylinder, or (4) both therod side of the upper hydraulic cylinder and the blind side of the lowerhydraulic cylinder. The state in which none of the chambers ispressurized does not produce any force on the working piston, nor (foridentical cylinders) does the state in which all chambers arepressurized. In the embodiment depicted in FIG. 3A, each stage isconfigured with two liquid pumps that actuate one after the other, andbecause each liquid pump in this embodiment has four possible gears, thecompression process has eight possible gears. It is to be appreciatedthat other embodiments include those in which the hydraulic fluidpressure communicated to the various surface areas in actuator 312 maybe different from each other and may create more than four possiblegears in each liquid pump. It is appreciated that given an actuator thatcan achieve four possible gears, it may be preferable to use fewer gearsthan four gears, for example three gears. The reasons for such apreference may involve the dynamic response of the fluid and/ormechanical components to the gear shift events. Correspondingly, anembodiment configured with two liquid pumps may be operated using five,six, or seven of the possible eight gears. Moreover, the compressionprocess may also vary according to the current pressure of thecompressed air storage vessel, e.g. when the storage vessel is atrelatively low pressure, the preferred compression process may use one,two, three, four, five, six, or seven of the possible eight gears.

In other embodiments, an actuator can be configured to have a differentnumber of possible different gears and gear changes based on, forexample, the number of hydraulic cylinders, the size (e.g., diameter) ofthe housing of a hydraulic cylinder in which a hydraulic piston ismovably disposed, the size (e.g., diameter) of the hydraulic pistonsdisposed within the housing of the hydraulic cylinders, the number andsize of drive rods coupled to the hydraulic pistons, and/or the size ofthe working piston to be actuated. Other examples of actuators aredescribed in the Ingersoll I application incorporated by referenceabove.

Thus, the hydraulic pressure time profile can be varied as needed toachieve a particular output gas pressure. The efficiency range of thehydraulic pump system can determine the number of gears and gear shiftsthat may be needed for a desired gas pressure range (difference betweeninput or start pressure and output or end pressure). For example, if thehydraulic pump's efficiency range is narrower, then more gears may beneeded for a given gas pressure range. The size and number of gears canalso depend on the particular operating speed (RPM) of the system.

As discussed above, heat can be transferred from air (or other gas) thatis compressed in the working chamber to reduce the work consumed by thecompression process. Heat can be transferred from gas to a liquid,and/or gas to dividers within the working chamber, and/or from theliquid out of the working chamber. In some embodiments, to increase thetotal amount of heat energy transferred during each cycle, the systemcan be operated at a relatively slow speed. For example, in someembodiments, a complete compression or expansion cycle may be slowenough to provide sufficient time for enough heat energy to betransferred between the gas and the liquid to approximate an isothermalcompression and/or expansion process, achieving work reduction orextraction and the efficiencies associated therewith. Additionally oralternatively, faster speeds may allow larger power levels to beachieved during expansion, isothermally or with temperature changes,which may be desirable at particular times during the system operation.

The use of a liquid (e.g. water) as a medium through which heat passesduring compression and/or expansion may allow for a continuoustemperature moderation process and may provide a mechanism by which heatenergy may be moved in and/or out of the working chamber. That is,during compression the liquid may receive heat energy from gas that isbeing compressed, and pass this heat energy to the external environmentcontinuously, or in batches, both while gas is being compressed andwhile gas is being received by the working chamber for latercompression. Similarly, heat energy addition may occur when acompressor/expander device is operating in an expansion mode both duringexpansion and as expanded gas is passed from a pressure vessel.

As discussed above, the liquid within a pressure vessel can be incontact with the gas at one or more gas/liquid interfaces andgas/divider interfaces, across which heat energy is transferred from gasthat is compressed and/or to gas that is expanded. The pressurevessel/working chamber can also include a heat exchanger, such as one ormore heat pipes as discussed above, that transfers heat energy betweenthe liquid and an environment that is external to the device. Heatenergy may be moved from gas that is compressed and/or to gas that isexpanded to achieve isothermal or near isothermal compression and/orexpansion processes.

As described above, adiabatic compression assumes that no energy (heat)is transferred to or from the gas during the compression process, andall applied work is added to the internal energy of the gas, resultingin increases of both temperature and pressure. In contrast, isothermalcompression assumes that the compressed gas remains at a constanttemperature throughout the compression process, and energy is removedfrom the system at the same rate as heat is added by the mechanical workof compression. For a given gas volume reduction (i.e., ratio of finalvolume to initial volume), an adiabatic compression process results inthe highest final gas pressure, the highest final gas temperature, andthe highest work consumption. For the same volume reduction, anisothermal compression process results in the lowest final pressure andconsumes half of the work as the adiabatic compression process. Thedifference in the amount of mechanical work required is reflected in theheat energy that is retained in the compressed gas. This due to the factthat if there is no temperature difference throughout the process, theinternal energy (U) remains invariant. The equation below is asimplified version of the conservation of energy or the first law ofthermodynamics. If dU is zero, then the amount of heat transferred (dQ)equals the work input (dW).

dU=dQ−dW

for dU=0, dQ=dW

The use of adiabatic compression (or near adiabatic compression) may bedesirable in some applications since approximately twice as much energyis stored at the end of the compression process. However, sinceapproximately half of this stored energy is heat energy, and perfectinsulation is not practical, the heat energy will flow out of thecompressed gas over time. In applications where the compressed gas isgoing to be stored for a period of time, isothermal compression (or nearisothermal compression) may be desirable to prevent work from being lostin the form of heat energy flow out of the compressed gas over time. Forexample, in compressed gas energy storage, where a compressed gas ismoved out of a compression device to a storage structure for potentiallylonger term storage, minimizing the work lost due to heat flow out ofthe compressed gas/system may be desirable.

In the gas compression/expansion devices and systems described herein,the heat transfer characteristics can be varied to approximate nearadiabatic compression and/or expansion or near isothermal compressionand/or expansion, and anywhere in between those two theoretical limits.For example, as described above, heat energy can be removed from a gasduring a compression process (or can be added to a gas during anexpansion process) via a liquid that is present in one or more pressurevessels of a compressor/expander device to control the gas temperaturethroughout the process. In other examples, a heat transfer element canbe positioned within the interior of a working chamber of acompressor/expander device to provide sufficient gas/liquid interfaceand/or sufficient thermal capacity to efficiently intermediate in, andenhance, the transfer of heat between the gas and the liquid.

As described above, the rate at which heat energy is added to the gas asit is being compressed (or released from the gas during an expansionprocess) can also be varied to approximate near adiabatic compressionand/or expansion or near isothermal compression and/or expansion, andanywhere in between those to theoretical limits, by changing the rate atwhich mechanical work is being done on the gas (i.e., changing the speedof the compression/expansion stroke, or the rate of change of volume ofthe working chamber).

The following discussion compares the operation of acompression/expansion device as described herein. In each case, it isassumed that the same quantity of gas is compressed (or expanded) overthe same pressure ratio, the initial temperature of the gas is the samefor compression cycles, but the temperature of the gas is allowed tovary over the course of the compression cycle. Since the pressure ratiois held constant and only the temperature is allowed to vary, the ratioof the mechanical work done on the gas to the heat flow out of thesystem is relatively constant in these examples. Typically the pressurewill vary when the temperature is caused to change through the stroke,however these graphs keep pressure fixed to best illustrate theflexibility such a system can have by isolating a single variable fordiscussion purposes. That being said, it is possible to change thedischarge temperature while maintaining the same pressure profile bychanging the volumetric compression/expansion ratio. This is possiblewith the system described above by changing stroke length, and/orchanging the volume of water in the system. As will be apparent from thediscussion below, one or more of the system variables can be changed toachieve any desired temperature and pressure profile.

Each of FIGS. 5-11 is an example graph illustrating the operation of acompression and/or expansion device as described herein. The valuesshown in FIGS. 5-11 are exemplary and for comparisons purposes only andthe systems and methods described herein are not limited to the datadisclosed in these figures. FIG. 5 illustrates one example of acompressor/expander device designed and operated to achieve essentiallyisothermal compression. The pressure of a quantity of gas is raised froman initial pressure of 1 bar to a final pressure of 7 bar (i.e., 7:1pressure ratio) over a six second compression stroke. In this example,during the compression stroke, energy is continuously being transferredto a heat transfer element positioned within the interior of a workingchamber of a compressor/expander device. The energy is then transferredfrom the heat transfer element to a liquid (such as water) present inthe compressor/expander device. A portion of the liquid is then removedfrom the working chamber after the compression cycle has been completed,and transferred to another stage of the system and/or out of the systementirely. Heat energy is removed from the system at the same rate asheat energy is added by the mechanical work of compression, so thetemperature of the gas remains constant throughout the compressionstroke.

FIG. 6 illustrates another example of the operation of a compressionand/or expansion device where the pressure of a quantity of gas israised from an initial pressure of 1 bar to a final pressure of 7 bar(i.e., 7:1 pressure ratio) over a six second compression stroke. In thisexample, less liquid is removed from the working chamber after thecompression cycle has been completed, thus the heat transfer element isnot “reset” to the initial temperature of the incoming gas. The heattransfer rate is a function of the temperature differential between thegas being compressed and the heat transfer element, therefore the heattransfer rate will be lower in this example than in the isothermalexample shown in FIG. 5. Since the heat transfer rate is lower, and lessheat energy is being removed from the system (i.e., less heated liquid)than is being added by the mechanical work of compression, thetemperature of the gas rises, in this example at a relatively linearrate throughout the compression stroke. The rate at which thetemperature of the gas rises related to the volume of liquid removedfrom the working chamber after the compression cycle has been completed.

FIG. 7 illustrates another example of the operation of a compressionand/or expansion device where the pressure of a quantity of gas israised from an initial pressure of 1 bar to a final pressure of 7 bar(i.e., 7:1 pressure ratio) over a six second compression stroke. Asdescribed above, the configuration (size, shape, structure, etc.) of theheat transfer element can be changed to vary the surface area per unitvolume or mass within the gas as it is being compressed/expanded duringa compression/expansion cycle. In this example, the heat transferelement has multiple components that are movable with respect to eachother such that the volumetric density of the heat transfer element canbe varied as a function of stroke throughout the compression cycle. Thevarying density at different times during the compression cycle changesthe heat transfer rates throughout the compression cycle. As shown, thetemperature profile resembles a polynomial function, which may bedesirable for processes where the temperature profile is of interest(e.g., a chemical reaction process), and not just the initial and finaltemperature.

FIG. 8 illustrates another example of the operation of a compressionand/or expansion device where the pressure of a quantity of gas israised from an initial pressure of 1 bar to a final pressure of 7 bar(i.e., 7:1 pressure ratio). In this example, the liquid removal rate andthe heat transfer element configuration are the same as the exampleshown in FIG. 5, however the compression stroke has been shortened to 3seconds. As described above, the rate at which heat energy is added tothe gas as it is being compressed (or released from the gas during anexpansion process) can be varied by changing the rate at whichmechanical work is being done on the gas (i.e., changing the speed ofthe compression/expansion stroke). By doubling the speed of thecompression stroke, approximately the same amount of work is being doneon the gas in half the time, thus increasing the rate at which heatenergy is added to the gas as it is being compressed. Since the heattransfer element geometry and materials have not changed, the maximumrate at which heat is transferred to or from the gas has not changed.Therefore the increased rate of heat transfer necessary with a shorterstroke is not adequately met by the same geometry as was used in FIG. 5.This results in the rise in temperature seen in FIG.8 that was not seenin FIG. 5.

FIG. 9 illustrates another example of the operation of a compressionand/or expansion device where the pressure of a quantity of gas israised from an initial pressure of 1 bar to a final pressure of 7 bar(i.e., 7:1 pressure ratio) over a six second compression stroke. In thisexample, the effects of decreasing the amount of liquid (FIG. 6) that isremoved from the working chamber after the compression cycle and ofchanging the configuration of the heat transfer element (FIG. 7) can becombined or superimposed, allowing a different temperature profile to beachieved than can be achieved with either effect separately. In realitythe effects are not a simple summation of two separate effects, howeverit is a good first approximation and serves to illustrate thephenomenon.

FIG. 10 illustrates an example of the operation of a compression and/orexpansion device where the pressure of a quantity of gas is raised froman initial pressure of 1 bar to several final pressures isothermally at300 K. It is possible to size a heat transfer element such that severaldifferent pressure profiles all result in a near-isothermal process asshown in FIG. 10. Such a change can be effected in process withoutmodification to the geometry and without shutting down the system. Itcan be appreciated that the temperature profile can be simultaneouslyaltered in the manners shown in FIG. 5-9 at the same time the pressureprofile is customized as shown in FIG. 10.

FIG. 11 illustrates another example of the operation of a compressionand/or expansion device where the pressure of a quantity of gas islowered from an initial pressure of 7 bars to a final pressure of 1 bar(i.e., 7:1 pressure ratio) over a three second compression stroke. Inthis example, the liquid removal rate and the heat transfer elementconfiguration are the same as the example shown in FIG. 8, however thecompressor/expander device is operating in an expansion cycle. It is tobe appreciated that although FIGS. 5-10 illustrate the operation of acompression and/or expansion device during a compression cycle, thechanges to the system variables illustrated in those examples areequally applicable to an expansion cycle.

FIG. 12 schematically illustrates a portion of a compressor/expanderdevice according to another embodiment. A compressor/expander device 400can include one or more pressure vessels (cylinders) 420 having a firstworking chamber 462 and a second working chamber 464, an actuator 421connected to a piston 466 via a piston rod 427, and first heat transferelement 423 and a second heat transfer element 425 disposed within thepressure vessel 420. The compression/expansion device 400 can be used inthe same or similar manner as described above for previous embodiments,to compress and/or expand a gas (e.g., air). In this embodiment, thepiston 466 is used to move a liquid within the pressure vessel 420 tocompress and/or expand a gas within the pressure vessel 420.

More specifically, the first heat transfer element 423 is disposedwithin the first working chamber 462 and the second heat transferelement 425 is disposed within the second working chamber 464. Thecompressor/expander device 400 can be used, for example, to compressand/or expand a gas, such as air, within the first working chamber 462or the second working chamber 464. The compressor/expander device 400can be used, for example, in a CAES system. The pressure vessel 420 caninclude an inlet conduit 428 and an outlet conduit 429 in fluidcommunication with the first working chamber 462 and an inlet conduit430 and an outlet conduit 431 in fluid communication with the secondworking chamber 464. The first working chamber 462 and the secondworking chamber 464 can contain, at various time periods during acompression and/or expansion cycle, a quantity of the gas (e.g., air)and a quantity of the liquid (e.g., water) that can be communicated toand from the working chambers via the inlet/outlet conduits. Optionally,the pressure vessel 420 can include one or more additional conduits influid communication with the first working chamber 462 or the secondworking chamber 464 specifically dedicated to communicating gas orliquid to or from the first and second working chambers 462, 464. Thecompressor/expander device 400 can also include multiple valves (notshown in FIG. 12) coupled to the inlet/outlet conduits 428, 429, 430,and 431 and/or to the pressure vessel 420. The valves can be configuredto operatively open and close the fluid communication to and from theworking chambers 462 and 464. Examples of use of such valves aredescribed in more detail in the Compressor and/or Expander Deviceapplications incorporated by reference above.

The actuator 465 can be any suitable mechanism for causing reciprocalmovement of the piston 466 within the pressure vessel 420. As the piston466 is moved back and forth within the pressure vessel 420, the volumeof the first working chamber 462 and the second working chamber 464and/or the portion of the volume of the first working chamber 462 andthe second working chamber 464 that can be occupied by gas can beselectively changed. The actuator 465 can be for example, an electricmotor or a hydraulically driven actuator such as, for example, thehydraulic actuators described in the Ingersoll I applicationincorporated herein by reference above. The actuator 465 can be coupledto the piston 466 via the piston rod 427 and used to move the piston 466back and forth within the interior region of the pressure vessel 420.For example, the working chamber 462 can be defined by the cylinder 420and the bottom face of piston 466. Similarly, the working chamber 464can be defined by the cylinder 420 and the top face of the piston 466.In this manner, the piston 466 is movably disposed within the interiorregion of the cylinder 420 and can divide the interior region between afirst interior region (working chamber 462) and a second interior region(working chamber 464).

As the piston 466 moves back and forth within the interior region of thecylinder 420, a volume of the first working chamber 462 and a volume ofthe second working chamber 464 will each change. For example, the piston466 can be moved between a first position (e.g., top dead center) inwhich the first working chamber 462 includes a volume of fluid greaterthan a volume of fluid in the second working chamber 464, and a secondposition (e.g., bottom dead center) in which the second working chamber464 includes a volume of fluid greater than a volume of fluid in thefirst working chamber 462. As used herein, “fluid” means a liquid, gas,vapor, suspension, aerosol, or any combination of thereof. At least oneseal member (not shown), such as, for example, a rolling seal member canbe disposed within the first working chamber 462 and the second workingchamber 464 of the cylinder 420 and can be attached to the piston 466.The arrangement of the rolling seal member(s) can fluidically seal thefirst working chamber 462 and the second working chamber 464 as thepiston 466 moves between the first position (i.e., top dead center) andthe second position (i.e., bottom dead center). Examples and use of arolling seal member are described in more detail U.S. patent applicationSer. No. 13/312,467 to Ingersoll et al. (“the Ingersoll IIIapplication”), entitled “Compressor and/or Expander Device with RollingPiston Seal,” the disclosure of which is incorporated herein byreference in its entirety

In some embodiments, the piston 466 is moved within the pressure vessel420 to compress a gas, such as air, within the pressure vessel 420. Insome embodiments, the piston 466 can be configured to be single-acting(e.g., actuated in a single direction to compress and/or expand gas). Asshown in FIG. 12, the compressor/expander device 400 is configured to bedouble-acting in that the piston 466 can be actuated in two directions.In other words, the piston 466 can be actuated to compress and/or expandgas (e.g., air) in two directions. For example, in some embodiments, asthe piston 466 is moved in a first direction, a first volume of a fluid(e.g., water, air, and/or any combination thereof) having a firstpressure can enter the first working chamber 462 of the cylinder 420 onthe bottom side of the piston 466. In addition, a second volume of thefluid having a second pressure can be compressed by the top side of thepiston 466 in the second working chamber 464. The gas portion of thesecond volume of fluid can then exit the second working chamber 464.When the piston 466 is moved in a second direction opposite the firstdirection, the gas portion of the first volume of fluid within the firstworking chamber 462 can be compressed by the piston 466. The gas portionof the first volume of fluid can then exit the first working chamber 462having a third pressure greater than the first pressure, andsimultaneously a third volume of fluid can enter the second workingchamber 464.

The heat transfer element 423 disposed within the first working chamber462 and the heat transfer element 425 disposed within the second workingchamber 464 can be a variety of different configurations, shapes, sizes,structures, etc. to provide a relatively high surface area per unitvolume or mass that can be in contact with the gas (e.g., air) as it isbeing compressed or expanded. In this embodiment, as shown in FIG. 8,the heat transfer element 423 is disposed near the bottom surface of thepiston 466 and the heat transfer element 425 is disposed at a topportion of the second working chamber 464. In some embodiments, the heattransfer element 423 disposed within the first working chamber 462 canbe attached to the bottom face of the piston 466. Similarly, in someembodiments, the heat transfer element 425 disposed within the secondworking chamber 464 can be attached to the top face of the piston 466,as described in further detail herein. In such embodiments, the heattransfer elements 423, 425 can move with the piston 466 as it isactuated.

In some embodiments, it may be desirable to form the heat transferelements 424 with a material that can provide high thermal conductivity.For example, the heat transfer elements 424 (i.e., the heat transferelement 423 and the heat transfer element 424) can be formed with metals(e.g. stainless steel) in the form of, for example, sheet or wire,carbon fiber, nano-materials, and hybrid or composite materials (e.g.carbon polymer compounds) which have anti-corrosion properties, arelighter weight, and are less expensive than some metallic materials.

The compressor/expander device 400 also includes an actuator 421 and anactuator 422 that can each be configured the same as, or similar to,actuator 122 a described above. The actuators 421 and 422 can eachinclude a piston (not shown) disposed within a housing (not shown). Theactuator 422 can be actuated to move liquid between the housing and thefirst working chamber 462 via a liquid inlet/outlet 433, and theactuator 421 can be actuated to move liquid between the housing and thesecond working chamber 464 via a liquid inlet/outlet 435. The pistons ofthe actuators 421 and 422 can each be coupled to, for example, anelectric motor or hydraulic actuator configured to actuate the pistons.

The compression/expansion device 400 can also include a first liquidoutlet 468 coupled to, and in fluid communication with, a liquid purgesystem 438 and the first working chamber 462, and a second liquid outlet470 coupled to, and in fluid communication with, the liquid purge system438 and the second working chamber 464. The liquid purge system 438 canbe configured the same as or similar to, and function the same as orsimilar to, the liquid purge systems 238 and 338 described above. Thefirst liquid outlet 468 can be opened to evacuate a volume of the liquidfrom the first working chamber 462, and the second liquid outlet 470 canbe opened to evacuate a volume of the liquid from the second workingchamber 464, as described above for previous embodiments.

The liquid purge system 438 can include a first pump (not shown) coupledto, and in fluid communication with, the first liquid outlet 468, and afirst conduit (not shown) coupled to, and in fluid communication with, athermal management facility (not shown). The liquid purge system 438 canalso include a second pump (not shown) coupled to, and in fluidcommunication with, the second liquid outlet 470, and a second conduit(not shown) coupled to, and in fluid communication with, the thermalmanagement facility. The pumps can each be actuated to move liquid fromthe first working chamber 462 and the second working chamber 464 to thethermal management facility. The thermal management facility can includea pump (not shown) configured to pump cooled liquid to the actuator 421and 422. In some embodiments, the liquid purge system 438 and actuators421 and 422 can be subsystems of a liquid management system thatincludes a thermal management facility.

In use, when the piston 466 is actuated to compress a gas within thepressure vessel 420, the actuator 465 can be controlled to maintain arelatively constant pressure change profile throughout the stroke of thepiston 466. For example, when the piston 466 is actuated to compress aquantity of gas within the second working chamber 464, the piston 466can be actuated over a first distance at a first stroke speed and over asecond distance at a second stroke speed. The first distance and thesecond distance can be the same or different and the first stroke speedand the second stroke speed can be the same or different depending onany of a variety of factors including, for example, the presence orabsence of a liquid in the second working chamber 464, the presence orabsence of a heat transfer element 425 in the second working chamber464, the interaction between a volume of liquid and a heat transferelement 425 in the second working chamber, or the change in density ofthe heat transfer element 425 over the vertical distance of the pressurevessel. Said another way, as the piston 466 is actuated at the beginningof a compression stroke, a volume of liquid contained in the secondworking chamber 464 may not be in contact with the heat transfer element425 and the piston can be actuated over the first distance at the firststroke speed to maintain a relatively constant compression rate of thequantity of the because the surface are of the liquid acting on the gasis substantially equal to the surface area of the piston 466. As theliquid in the second working chamber 464 contacts and moves into theheat transfer element 425, the surface area of the liquid acting on thegas is reduced because the heat transfer element 425 occupies a portionof the cross-sectional area of the pressure vessel. Thus, in order tomaintain a relatively constant compression rate of the quantity of gas,the piston 466 can be actuated at a second stroke speed slower than thefirst stroke speed. As the compression stroke progresses, the strokespeed can be modified to maintain a relatively constant compression ratedepending on the structure (e.g., density) of the heat transfer element425 or to change the rate of compression. Similarly, the stroke speedcan be modified to maintain a relatively constant heat transfer rate outof the quantity of gas as it is being compressed or to manage thetemperature of the gas throughout the compression stroke to any desiredprofile as described herein.

While various embodiments of the invention have been described above, itshould be understood that they have been presented by way of exampleonly, and not limitation. Where methods and steps described aboveindicate certain events occurring in certain order, those of ordinaryskill in the art having the benefit of this disclosure would recognizethat the ordering of certain steps may be modified and that suchmodifications are in accordance with the variations of the invention.Additionally, certain of the steps may be performed concurrently in aparallel process when possible, as well as performed sequentially asdescribed above. The embodiments have been particularly shown anddescribed, but it will be understood that various changes in form anddetails may be made.

For example, although various embodiments have been described as havingparticular features and/or combinations of components, other embodimentsare possible having any combination or sub-combination of any featuresand/or components from any of the embodiments described herein. Forexample, although certain embodiments of a heat transfer element wereshown and described with respect to a particular embodiment of acompression/expansion device, it should be understood that the variousembodiments of a heat transfer element including, for example, rods,tubes, fins, fibers, filaments, coils, plates, mesh, etc. can be used inany of he various embodiments of a compression and/or expansion devicedescribed herein and in other embodiments of a compress and/or expansiondevice not described herein. Additionally, the specific configurationsof the various components of a compression and/or expansion device canalso be varied. For example, the size and specific shape of the variouscomponents can be different than the embodiments shown, while stillproviding the functions as described herein.

Although the liquid in the compressor/expander devices was describedabove as including water, other liquids can be used, additionally oralternatively. As is to be appreciated, water may naturally condense outof air that is being compressed by the system, and in this respect, maycombine with the liquid without adverse impact. Additionally, when usedin embodiments of the expander/compressor devices, water may evaporateinto air during expansion without having an adverse impact. Other typesof liquids, however, may be used in addition to or in place of water.Some examples of such liquids may include additives or entire liquidsformulated to prevent freezing, such as glycol, liquids that preventevaporation, such as glycerin, and/or liquids to prevent foaming.Similarly, although the gas in the compressor/expander device wasdescribed above as being air (which is a convenient choice, so thatambient air can be used), other gases can be used, additionally oralternatively.

In addition, although the system 300 was described as having two stageseach with two liquid pumps, and the liquid pumps are each actuated bytwo hydraulic actuators (an upper and a lower hydraulic actuator), inalternative embodiments, more hydraulic actuators can be coupled to thetop and bottom of a liquid pump, which can provide additional possiblegear modes. In addition, in other embodiments, a system can beconfigured with a different number of liquid pumps and/or a differentnumber of stages, which can provide additional possible gear modes. Inaddition, the systems and methods described herein can be controlledusing known computer systems and control system used for such purposes.

The system controller (e.g., 316) can include, for example, aprocessor-readable medium storing code representing instructions tocause a processor to perform a process. The processor can be, forexample, a commercially available personal computer, or other computingor processing device that is dedicated to performing one or morespecific tasks. For example, the processor can be a terminal dedicatedto providing an interactive graphical user interface (GUI). Theprocessor, according to one or more embodiments, can be a commerciallyavailable microprocessor. Alternatively, the processor can be anapplication-specific integrated circuit (ASIC) or a combination ofASICs, which are designed to achieve one or more specific functions, orenable one or more specific devices or applications. In yet anotherembodiment, the processor can be an analog or digital circuit, or acombination of multiple circuits.

The processor can include a memory component. The memory component caninclude one or more types of memory. For example, the memory componentcan include a read only memory (ROM) component and a random accessmemory (RAM) component. The memory component can also include othertypes of memory that are suitable for storing data in a form retrievableby the processor. For example, electronically programmable read onlymemory (EPROM), erasable electronically programmable read only memory(EEPROM), flash memory, magnetic disk memory, as well as other suitableforms of memory can be included within the memory component. It isrecognized than any and all of these memory components can be accessedby means of any form of communication network. The processor can alsoinclude a variety of other components, such as for example,co-processors, graphic processors, etc., depending upon the desiredfunctionality of the code.

The processor can be in communication with the memory component, and canstore data in the memory component or retrieve data previously stored inthe memory component. The components of the processor can be configuredto communicate with devices external to the processor by way of aninput/output (I/O) component. According to one or more embodiments, theI/O component can include a variety of suitable communicationinterfaces. For example, the I/O component can include, for example,wired connections, such as standard serial ports, parallel ports,universal serial bus (USB) ports, S-video ports, local area network(LAN) ports, small computer system interface (SCCI) ports, analog todigital interface input devices, digital to analog interface outputdevices, and so forth. Additionally, the I/O component can include, forexample, wireless connections, such as infrared ports, optical ports,Bluetooth® wireless ports, wireless LAN ports, or the like. Theprocessor can also be connected to a network, which may be any form ofinterconnecting network including an intranet, such as a local or widearea network, or an extranet, such as the World Wide Web or theInternet. The network can be physically implemented on a wireless orwired network, on leased or dedicated lines, including a virtual privatenetwork (VPN).

1. An apparatus, comprising: a hydraulic pump operable to deliverhydraulic fluid over at least a hydraulic pressure range that includes apredetermined lower pressure and a predetermined upper pressure, greaterthan said lower pressure; a hydraulic actuator arrangement including afirst hydraulic piston and a second hydraulic piston, each of saidhydraulic pistons having a first side and a second side; and a workingactuator operably coupled to said hydraulic actuator arrangement, saidworking actuator having a working cylinder and a working piston disposedfor reciprocating movement in the working cylinder, the working pistondefining at least in part between a first side thereof and the workingcylinder a working chamber configured to contain a quantity of gas, saidhydraulic actuator arrangement being operably coupled to said hydraulicpump to enable selective delivery of pressurized hydraulic fluid fromsaid hydraulic pump to one or both of said first side and said secondside of each of said first and second hydraulic pistons to yield anoutput force in a first force range corresponding to a firstcombination, and to yield an output force in a second force range,different than said first force range, corresponding to a secondcombination; a hydraulic controller operable to cause the hydraulicactuator arrangement to move the working piston: a) at a first averagespeed over a first distance, and b) at a second average speed over asecond distance different than the first average speed, wherein thehydraulic controller is operable to compress the quantity of gascontained therein at an approximately constant rate as the workingpiston is moved over the first distance at the first stroke speed andthe second distance at the second stroke speed.
 2. The apparatus ofclaim 1, further comprising: a heat transfer element disposed within theworking chamber, the heat transfer element configured to receive heatenergy from the gas being compressed to reduce the temperature of thecompressed gas.
 3. The apparatus of claim 2, wherein the heat transferelement is configured to transfer heat energy received from thecompressed gas to the exterior of the working chamber.
 4. The apparatusof claim 2, wherein the heat transfer element is configured to transferheat energy received from the compressed gas to a volume of liquidcontained in the working chamber.
 5. The apparatus of claim 4, whereinthe volume of liquid is not in contact with the heat transfer elementduring movement of the working piston over the first distance.
 6. Theapparatus of claim 5, wherein at least a portion of the volume of liquidis in contact with at least a portion of the heat transfer elementduring movement of the working piston over the second distance.
 7. Theapparatus of claim 1, wherein the first stroke speed corresponds to thefirst force range and the second stroke speed corresponds to the secondforce range.
 8. An apparatus, comprising: a hydraulic pump operable todeliver hydraulic fluid over at least a hydraulic pressure range thatincludes a predetermined lower pressure and a predetermined upperpressure, greater than said lower pressure; a hydraulic actuatorarrangement including a first hydraulic piston and a second hydraulicpiston, each of said hydraulic pistons having a first side and a secondside; and a working actuator operably coupled to said hydraulic actuatorarrangement, said working actuator having a working cylinder and aworking piston disposed for reciprocating movement in the workingcylinder, the working piston defining at least in part between a firstside thereof and the working cylinder a working chamber configured tocontain a quantity of gas, said hydraulic actuator arrangement beingoperably coupled to said hydraulic pump to enable selective delivery ofpressurized hydraulic fluid from said hydraulic pump to one or both ofsaid first side and said second side of each of said first and secondhydraulic pistons to yield an output force in a first force rangecorresponding to a first combination, and to yield an output force in asecond force range, different than said first force range, correspondingto a second combination; a hydraulic controller operable to cause thehydraulic actuator arrangement to move the working piston: a) at a firstaverage speed over a first distance, and b) at a second average speedover a second distance different than the first average speed, whereinthe hydraulic controller is operable to compress the quantity of gascontained therein such that heat energy produced by compression of thequantity of gas is transferred from the quantity of gas to the exteriorof the working chamber at a substantially constant rate as the workingpiston is moved over the first distance at the first stroke speed andthe second distance at the second stroke speed.
 9. The apparatus ofclaim 8, further comprising: a heat transfer element disposed within theworking chamber, the heat transfer element configured to receive heatenergy from the gas being compressed to reduce the temperature of thecompressed gas.
 10. The apparatus of claim 9, wherein the heat transferelement is configured to transfer heat energy received from thecompressed gas to the exterior of the working chamber.
 11. The apparatusof claim 9, wherein the heat transfer element is configured to transferheat energy received from the compressed gas to a volume of liquidcontained in the working chamber.
 12. The apparatus of claim 8, whereinthe heat energy produced by compression of the quantity of gas istransferred from the quantity of gas to the exterior of the workingchamber to maintain a substantially constant temperature duringcompression of the quantity of gas.
 13. A method of compressing gas in apressure vessel, the pressure vessel having a working piston disposedtherein for reciprocating movement in the pressure vessel, the workingpiston defining at least in part between a first side thereof and thepressure vessel a working chamber configured to contain at least one ofa liquid or a gas, the method comprising: moving the working piston at apredetermined velocity profile to compress a quantity of gas containedtherein so that the time rate of change of pressure is approximatelyconstant over substantially the entire stroke.
 14. The method of claim13, wherein the working chamber includes a heat transfer elementdisposed therein, and wherein the predetermined velocity profile isdetermined by taking into account the portion of the cross-sectionalarea occupied by the heat transfer element.
 15. The method of claim 13,further comprising: moving a volume of liquid into the working chamberduring at least a portion of a compression stroke, wherein thepredetermined velocity profile is determined by taking into account thevolume of liquid being received in the working chamber.
 16. The methodof claim 13, wherein the working chamber includes a heat transferelement disposed therein, the method further comprising: moving a volumeof liquid into the working chamber during at least a portion of acompression stroke, wherein the predetermined velocity profile isdetermined by taking into account the portion of the cross-sectionalarea occupied by the heat transfer element and the volume of liquidbeing received in the working chamber.
 17. The method of claim 13,further comprising: causing heat energy produced by the compression ofthe quantity of gas to be transferred from the quantity of gas to theexterior of the working chamber so that a predetermined temperatureprofile during compression of the quantity of gas is maintained.
 18. Themethod of claim 17, wherein the rate of temperature change isapproximately constant over substantially the entire stroke.
 19. Themethod of claim 13, wherein the working chamber includes a heat transferelement disposed therein, the method further comprising: causing thetemperature of the quantity of gas to increase to a temperature above atemperature of the heat transfer element, and causing heat energyproduced by the compression of the quantity of gas to be transferredfrom the quantity of gas to the heat transfer element.
 20. The method ofclaim 19, wherein the predetermined velocity profile is determined bytaking into account a rate at which heat energy produced by compressionof the quantity of gas is transferred from the quantity of gas to theheat transfer element so that a predetermined temperature profile of thegas is maintained.